This invention relates to optical switching, e.g., reconfigurably interconnecting multiple optical input signals to multiple optical output signals.
Optics and photonics are finding many applications in modern technology, including, e.g., optical communication, optical computing, and visual displays. In such applications, light beams carry information as optical signals. Often it is necessary to dynamically redirect one or more of such light beams to one or more selected targets. For example, operators of fiber optic networks typically manage bandwidth demands, channel redundancy, and channel faults by reconfiguring fiber optic pathways at one or more switching nodes.
A module for redirecting one or more optical input signals to one or more optical output signals is known as an optical crossbar switch. For example, an Mxc3x97N optical crossbar switch reconfigurably connects each of M optical input channels to none, one, or many of N optical output channels. In some cases, M equals N, while in other cases, M is not equal to N. Such a device may include a spatial light modulator (SLM) having at least M by N independently addressable elements for controlling reflection and/or transmission. For example, input optics can be used to fan-out the output of each of a horizontal array of emitters onto a corresponding column of the SLM. Output optics can then be used to fan-in the output from each row of the SLM to a corresponding one of a vertical array of detectors.
The invention features a compact and versatile optical crossbar switch that exploits the properties of a diffractive optical element (DOE). The diffractive optical element is a substrate having multiple diffractive patterns. Each diffractive pattern causes an incident beam to be directed along a selected direction. As a result, the DOE can steer multiple beams along multiple, separate directions. Because the multiple diffractive patterns that provide such beam steering can be made on a single substrate, the DOE is also small and compact. The optical crossbar switch combines the DOE with a spatial light modulator (SLM) having multiple addressable elements.
The DOE permits more compact and versatile optical arrangements for the SLM. In particular, the DOE element can redirect multiple light signals modulated by the SLM to accommodate multiple, spatially separated target locations. Moreover, because the DOE can be used to accommodate such multiple target locations, the SLM can also accommodate many input arrangements for the optical beams incident on the SLM. In particular, input arrangements may be selected that better exploit the spatial extent of the SLM. For example, each input optical signal may illuminate a circular or elliptical section of the SLM, as an alternative to a section of the SLM having a high aspect ratio, such as a row or column. Moreover, such illuminated circular or elliptical sections of the SLM may be closely packed, e.g., as a hexagonal array, to thereby optimize the throughput of the SLM. Any of the above features may improve packaging constraints on a module incorporating the optical crossbar switch. Furthermore, in embodiments where the elements of the SLM may themselves redirect incident beams (e.g., a MEMS device), the DOE can compound such redirection, thereby expanding the dynamic range of the SLM.
The optical crossbar switch including the DOE can be used in a WDM fiber optic network for reconfiguring fiber optic channels, as well as in other applications, such as dynamic three-dimensional displays.
In general, in one aspect, the invention features an optical crossbar switch system. The system includes: a mask including multiple patterns, wherein at least one of the multiple patterns is a diffractive pattern; and a spatial light modulator positioned to receive one or more optical input beams and selectively couple at least a portion of each optical input beam to one of the patterns of the mask. Each coupled portion defines an intermediate beam, and each pattern, when selected by the spatial light modulator, is configured to redirect the intermediate beam to one of N targets, where N is an integer greater than two.
Embodiments of the optical crossbar switch system may include any of the following features.
There may be only one optical input beam, and the multiple patterns may include N patterns. Furthermore, there may be a one-to-one correspondence between the N patterns and the N targets, and each pattern, when selected by the spatial light modulator, is configured to redirect the intermediate beam to the corresponding target.
Alternatively, there may be M optical input beams, where M is an integer greater than one. Moreover, the mask may include M regions, each pattern being in one of the M regions. Furthermore, there may be a one-to-one correspondence between the M input beams and the M regions, with the spatial light modulator positioned to selectively couple each of the input beam portions to the corresponding region of the mask. Also, there may be MxN patterns, with each region of the mask including N of the patterns. Furthermore, there may be a one-to-one correspondence between the N patterns in each region of the mask and the N targets, with each pattern in each region, when selected by the spatial light modulator, configured to redirect the intermediate beam to the corresponding target. In any of such embodiments, M may be equal to N, or M may be different from N.
The modulator may include an array of multiple elements. The multiple elements may be individually, electronically controllable to cause the spatial light modulator to selectively couple each of the input beam portions to the corresponding one of the multiple patterns. The multiple elements may include a reflective component having an adjustable orientation. Alternatively, the multiple elements may adjustably vary the magnitude of transmission or reflection of an incident beam. The multiple elements may include a liquid crystal cell, e.g., to adjustably vary the polarization of an incident beam. In addition to the liquid crystal cell, the elements may include one or more polarizers. The crossbar system may further include an electronic processor coupled to the spatial light modulator to cause the modulator to selectively couple the input beam portions to the corresponding one of the multiple patterns. The array of multiple elements may be, e.g., a one-dimensional array, a two-dimensional array, or a hexagonal array.
The spatial light modulator may be positioned to receive each of the one or more input beams on, for example, a substantially circular section of the elements, or along a row or column of the elements.
The mask may be a prefabricated to include fixed patterns. Alternatively, the mask itself may be a spatial light modulator providing reconfigurable patterns. At least some of the multiple patterns of the mask may be diffractive patterns. For example, all of the multiple patterns of the mask may be diffractive patterns. The patterns on the mask may be spatially separated from one another.
The diffractive pattern may be a transmissive or reflective diffractive pattern, for example, a transmissive or reflective grating pattern. The grating pattern may be optimized for a particular order of diffraction, e.g., for first order diffraction. The grating pattern may be, e.g., a blazed grating pattern or a holographic grating pattern. The diffractive pattern may include phase-modulation, amplitude-modulation, or phase-modulation and amplitude modulation. The diffractive pattern may be defined, e.g., by an etched pattern on the mask or by a coated pattern on the mask.
The mask may be flat or curved.
The system may further include an intermediate optic positioned between the spatial light modulator and the mask. For example, the intermediate optic may be a mirror, a lens, a microlens array, a polarizer, a wave plate, or a beam splitter. The system may further including a source for the input optical beam(s). Furthermore, the system may include an intermediate optic positioned between the source and the spatial light modulator. Again, for example, the intermediate optic may be a mirror, a lens, a microlens array, a polarizer, a wave plate, or a beam splitter.
The source of the input beams may include an array of optical input fibers, each fiber carrying one of the optical input beams. It may further include a laser source optically coupled to the optical fiber array.
The M optical input beams may each have a different wavelength, and their source may include an input fiber carrying optical signals at different wavelengths and a wavelength division demultiplexer optically coupled to the fiber for separating the optical signals into at least some of the M optical input beams. The source may further include a laser source optically coupled to the fiber.
The system may further include an array of N optical output fibers, which define the N targets. Alternatively, for example, the system may further include an array of N detectors, which define the N targets. Also, the system may further include a wavelength division multiplexer having N inputs, which define the N targets, and an output fiber coupled to the wavelength division multiplexer for carrying optical signals derived from the output beams.
In another aspect, the invention features a method for selectively coupling each of one or more input beams to one of multiple output channels. The method includes: selectively coupling at least a portion of each input beam to one of multiple patterns on a mask; and diffracting at least one of the coupled portions from the mask to one of the output channels. A spatial light modulator may be used to do the selectively coupling step. Embodiments of the method may further include any of the features described above with respect to the optical crossbar system.
Other features, aspects, and advantages follow.